On-going environmental concerns have resulted in increasingly stringent government regulations placed upon the automotive industry. One area of concern is the release of volatile hydrocarbon fuel vapors during refueling of a vehicle. A conventional vapor recovery system is described in U.S. Pat. No. 5,960,817, filed Nov. 3, 1997, and is incorporated herein by reference. When filling a fuel tank with volatile hydrocarbon fuel (or even diesel fuel), the air and fuel vapor in the tank is in-part filtered and displaced to atmosphere. Fuel vapor is removed from the displaced air before release to atmosphere by a fuel vapor storage canister that contains activated charcoal for absorbing the hydrocarbon vapors flowing from the fuel tank and later generally releasing the vapors to an intake manifold of an operating engine.
Other government regulations, directed toward emissions and fuel consumption, tend to persuade automotive manufacturers to produce lighter and smaller vehicles thus increasing fuel economy. Ideally, size and weight of every component, including the fuel vapor storage canister is addressed. Thus, the advantages of a larger and heavier canister to satisfy vapor regulations and prolong the operating life of a canister, can be outweighed by a smaller and lighter canister to satisfy fuel economy regulations and possibly reduce manufacturing costs provided, when necessary, alternative measures are taken to meet fuel vapor release regulations.
Because the useful operating life of a vapor storage canister is predicated on the amount and rate of vapor it must absorb during refueling, redirecting some of the fuel vapor otherwise exposed to the canister is one measure to prolong the life and reduce the necessary size and weight of a fuel vapor storage canister while still meeting government regulations. One such technique is a recirculation tube which communicates between the inlet side of the canister and a fill pipe that receives incoming liquid fuel from a remote fuel supply pump of a refueling station. The recirculation tube redirects a portion of the outgoing fuel vapor from the fuel tank during refueling of the tank and entrains the vapor into the incoming liquid fuel flowing within the fill pipe. To entrain the vapor into the liquid fuel and prevent release to atmosphere, the outlet aperture of the recirculation tube is located immediately downstream of a fill pipe restrictor plate designed to minimize splash-back of fuel and vapor release to atmosphere. The restrictor plate carries a hole sized to closely receive the fuel supply nozzle of the remote refueling pump.
Unfortunately, because the outlet aperture is located below the restrictor plate it is dependent upon the automatic shutoff feature of the remote fuel supply pump to prevent liquid fuel from entering the recirculation tube through the aperture. If the shutoff feature of the nozzle or remote fuel pump is not sufficiently responsive, or should the feature fail altogether, fuel backing up into the fill pipe can cause liquid fuel to enter the recirculation tube. The reverse flow of liquid fuel through the recirculation tube from the outlet aperture can degrade the vapor recovery system by potentially flooding the carbon canister and destroying the carbon bed.